A Brønsted acid catalyst for the enantioselective protonation reaction.

A highly reactive and robust chiral Brønsted acid catalyst, chiral N-triflyl thiophosphoramide, was developed. The first metal-free Brønsted acid catalyzed enantioselective protonation reaction of silyl enol ethers was demonstrated using this chiral Brønsted acid catalyst. The catalyst loading could be reduced to 0.05 mol % without any deleterious effect on the enantioselectivity.